Three patients will be accrued at each of 5 dose levels. Dose escalation will only proceed if none of the additional 3 patients experience DLT. The highest dose level that generates DLT in 0/3 or 1/6 patients will be the maximum tolerated dose (MTD) or the doses recommended for subsequent studies. A total of 10 patients will be treated at the MTD to further assess the toxicity of the dosing regimen and its suitability for use in subsequent trials. Patients may continue to receive treatment until unacceptable toxicity or disease progression is encountered. Treatment cycles will be repeated every 21 days. The protocol is also designed to enroll an additional 10 patients at the maximum tolerated dose to increase the confidence in the safety and suitability of the doses that are chosen for subsequent studies.